Technical Field
The present invention relates to a method and a device for cooling a steam turbine generating facility, which improves cooling effect of a dummy seal and a rotor shaft disposed inside of the dummy seal. The steam turbine generating facility is equipped with an opposed-flow single casing steam turbine in which a plurality of turbine parts are isolated from one another by a dummy seal and housed in a single casing.
Description of the Related Art
In response to the demand of more energy saving and environment preservation (CO2 reduction), steam turbine power plants are desired to have a larger capacity and improved thermal efficiency. The thermal efficiency is improved by raising the temperature and the pressure of working steam. The rotation of the turbine rotor generates high stress. Thus, the turbine rotor must withstand high temperature and high stress. While using the working steam of a higher temperature, a cooling technique of the turbine rotor is an important issue.
In accordance with the trend of increasing the capacity of the steam turbine power plants, there is a transition trend from a single-casing steam turbine power plant to a tandem compound steam turbine power plant. In the tandem compound steam turbine power plant, a high pressure turbine, an intermediate pressure turbine, a low pressure turbine and so on are individually housed in separate casings and each shaft of the turbines and the generator are coaxially joined.
This type of generating plant has at least one stage of repeaters in a boiler. The repeater reheats discharge steam having been discharged from each of the steam turbines to supply the reheated steam to the steam turbine on the low-pressure side. The rotor shafts of multiple stages of steam turbines are coaxially joined to the shaft of the generator so as to ensure the stability against the vibration of the rotor shafts.
In contrast, the steam turbine power plant of the tandem compound type adopts the structure of housing different pressure stages of steam turbines in a single casing. By reducing the number of casings, the axial length of the entire rotor can be shorter and the power plant can be downsized. For instance, in the opposed-flow single casing turbine, the high-pressure turbine and the intermediate-pressure turbine are housed in a single casing and dummy seals are interposed between the turbines. A steam supply path is provided across the dummy seal to supply working steam to each of the turbines. Each working steam is streamed in the casing as an opposed-flow to each blade cascade.
One example of the steam turbine power plant with the above structure is illustrated in FIG. 12. FIG. 12 shows a common steam turbine power plant that adopts a two-stage reheating system and has steam turbines of high intermediate pressure opposed-flow single casing type. Hereinafter, ultrahigh-pressure/very high pressure may be referred to as “VHP”, high and intermediate pressure may be referred to as “HIP” and low pressure may be referred to as “LP”.
FIG. 12 also shows a superheater 21 in a boiler 2. The superheater 21 produces steam. The steam is supplied to a VHP turbine 1 to drive the VHP turbine 1. The discharge steam from the VHP turbine 1 is reheated by a first-stage repeater 22 provided in the boiler to produce HP steam. The HP steam is supplied to a HP turbine part 31 of a HIP turbine of high and intermediate pressure opposed-flow single casing type to drive the HP turbine part 31.
Discharge steam from the HP turbine part 31 is reheated by a second-stage reheater 23 provided in the boiler 2 to produce IP steam. The IP steam is introduced to an IP turbine part 32 of the HIP turbine 3 to drive the IP turbine part 32. Discharge steam from the IP turbine part 32 is introduced to an LP turbine 4 via a crossover pipe 321 to drive the LP turbine 4. Discharge steam from the LP turbine 4 is condensed by a condenser 5, pressurized by a boiler supply pump 6 and then reheated by the superheater 21 of the boiler 21 to produce VHP steam. The VHP steam is circulated to the VHP turbine 1.
JP2000-274208 discloses a steam turbine of the opposed-flow single casing type in a steam turbine power plant of tandem compound type equipped with a boiler with two stage reheater. In the steam turbine of the opposed-flow single casing type, a VHP turbine and a HP turbine or the HP turbine and an IP turbine are housed in the single casing.
In a steam turbine such as the single-casing steam turbine and the high intermediate pressure opposed-flow single casing turbine, steam of high temperature without being used, enters a gap between the rotor shaft and the dummy seal that separates the HP turbine part and IP turbine part. By this, the dummy seal and the rotor shaft becomes exposed to a high temperature atmosphere. Thus, it is an important issue how to cool this area.
For instance in the single casing steam turbine such as the one shown in FIG. 2 to FIG. 5 of JP1-113101U (Utility Model Application) and the one shown in FIG. 2 of JP9-125909A, steam is supplied to the HP turbine part and passes a first-stage stator blades to a first-stage stator blade outlet. The steam out of the first-stage stator blade outlet is introduced to the IP turbine part through the gap between the dummy seal and the rotor shaft. The high temperature area of the dummy seal and the rotor shaft is cooled. The cooling method is described below in reference to FIG. 13.
FIG. 13 is a sectional view near a supply part of the working steam in the HIP turbine 3 of the steam turbine power plant of FIG. 12. In the HIP turbine 3 near the inlet for the HP steam and the IP steam in FIG. 13, a HP turbine blade cascade part 71, a HP dummy part (outer circumferential part) 72, an IP dummy part 73 and an IP turbine blade cascade part 74 are formed on an outer circumferential side of the turbine rotor 7. The HP turbine blade cascade part 71 has HP rotor blades 71a disposed at predetermined intervals. HP stator blades 8a of a HP blade ring 8 are arranged between the HP rotor blades 71a. At the most upstream part of the HP turbine blade cascade part 71, a HP first-stage stator blade 8a1 is arranged.
The IP turbine blade cascade part 74 has IP rotor blades 74a disposed at predetermined intervals. IP stator blades 9a of an IP blade ring 9 are arranged between the IP rotor blades 74a. At the most upstream part of the IP turbine blade cascade part 74, an IP first-stage stator blade 9a1 is arranged. A dummy ring 10 is provided between the HP blade ring 8 and the IP blade ring 9 to seal the HP turbine part 31 and the IP turbine part 32. Also, a seal fin part 11 is provided in places near the blade rings 8,9, the dummy ring 10 and the turbine rotor 7 so as to suppress the leaking of the steam to those parts.
The dummy ring 10 and the turbine rotor 7 are cooled by streaming a portion of the stream from the exit T of the first-stage stator blade 8a1 to an inlet of the IP turbine part 32. Specifically, the portion of the steam from the exit T of the first-stage stator blade 8a1 of the HP turbine streams between the HP dummy ring 72a and a HP dummy part of the rotor as HP dummy steam 72c. The HP dummy steam 72c then streams between the IP dummy ring 73a and an IP dummy part 73b of the rotor as HP dummy steam 73c. The IP dummy steam cools an inner surface of the IP dummy ring 73a and an IP inlet of the rotor 7.
A steam discharge path 10a is arranged in the dummy ring 10 in the radial direction. The HP dummy steam 72c is led by thrust balance through the steam discharge path 10a to a discharge steam pipe (unshown) of the HP turbine part 31 in the direction shown with an arrow 72d. 
In this structure, the steam temperature at the exit T of the first-stage stator blade 8a1 of the HP turbine part 31 must be lower than the steam temperature at the inlet of the first-stage stator blade 8a1 and at the inlet of the first-stage stator blade 9a1 of the IP turbine part to cool the area near the inlet part of the HP steam and the IP steam in the HIP turbine 3.
A two stage reheating turbine has VHP-HP-IP-LP structure in which the HP turbine part 31 and the IP turbine part 32 are housed in different casings. In the structure, the inlet parts of the HP turbine and the IP turbine are respectively cooled by the steam from each exit of the first-stage stator blade.
However, in a conventional steam turbine power plant, the steam expands through the HP first-stage stator bade 8a1 and is then used as cooling steam. Although the temperature is reduced, the steam from the first-stage stator blade 8a1 does not have high cooling effect with respect to the working steam streaming into the HP turbine 31.
In such a case that the steam temperature at the exit T of the first-stage stator blade of the HP turbine part 31 is not less than the steam temperature at the exit of the first-stage stator blade 9a1 of the IP turbine part, the steam from the first-stage stator blade 8a1 cannot be used as cooling steam for the IP turbine blade cascade part 74. The steam at the exit of the first-stage stator blade of the HP turbine part 31 is the steam before being used in the HP turbine blade cascade part 71 and thus, using the steam as cooling steam is a waste from a perspective of thermal efficiency.
In the single casing steam turbine illustrated in FIG. 1 of JP1-113101U (Utility Model Application), the discharge gas from a HP turbine part is partially supplied to an IP blade cascade part via a pipe 105 as cooling steam.
In the single casing steam turbine illustrated in FIG. 1 of JP9-125909A, the discharge gas from a HP turbine part is supplied to an inlet 44 of an IP turbine part via a thrust balance pipe 106 as cooling steam.
In the steam turbine of high intermediate pressure opposed-flow single casing type disclosed in JP11-141302A, the steam from first-stage rotor blades of a HP turbine part is supplied to a heat exchanger 16 to be cooled by heat exchange with low-temperature steam outside of the casing. The cooled steam is supplied as cooling steam to a clearance between a rotor shaft and a dummy seal isolating the HP turbine part and IP turbine part from each other.    JP2000-274208    JP1-113101U (Utility Model Application)    JP9-125909A    JP11-141302A